Emails published by Trump Jr on Tuesday showed that Goldstone promised the lawyer would bring from Russia “some official documents and information that would incriminate Hillary [Clinton]”. He said: “This is obviously very high level and sensitive information but is part of Russia and its government’s support for Mr Trump.”

Critics have said that the offer – and Trump Jr’s willingness to go ahead with the meeting – amount to proof of collusion. Trump Jr denies wrongdoing. On Tuesday evening, he told Fox News host Sean Hannity: “In retrospect I probably would have done things a little differently.” The meeting, he said, was “a nothing”.

On Wednesday, Trump Sr’s lawyer Jay Sekulow told morning TV shows the president did not find out about the meeting until “very recently”. Sekulow also said the president was not being investigated by Robert Mueller, the special counsel investigating links between Trump aides and Russia.

The New York Times reported, however, that Donald Trump signed off on his son’s first statement about the meeting, which said it was primarily about a Russian bar on US adoptions. The Times report cited anonymous sources. Trump also tweeted on Wednesday: “Remember, when you hear the words ‘sources say’ from the Fake Media, often times those sources are made up and do not exist.”

Trump’s firing of the FBI director James Comey in May is part of the Mueller investigation. The president’s pick to succeed Comey, Christopher Wray, appeared before the Senate judiciary committee on Wednesday. In his opening statement, Wray said he would “never allow the FBI’s work to be driven by anything other than the facts, the law and the impartial pursuit of justice. Period. Full stop.”

Answering questions, Wray said the Mueller investigation was not a “witch hunt” and said he would treat any attempt to tamper with it “very sternly”. In reference to reports Trump demanded loyalty from Comey, he said no one at the White House had asked him “for any kind of loyalty oath at any point during this process, and I sure as heck didn’t offer one”.

Russia’s foreign minister, Sergei Lavrov, said it was “wild” that Trump’s son was being blamed for speaking with a Russian attorney. Lavrov – who met Trump last week at the G20 summit in Hamburg, together with Vladimir Putin – said he knew nothing of the meeting with the lawyer. Serious people were trying to “make a mountain out of a molehill”, Lavrov said.

In the emails, Goldstone said he made contact with Trump Jr at the behest of the Russian-Azeri businessman Aras Agalarov and Aglaravov’s pop-star son, Emin. The Agalarovs hosted Trump when he visited Moscow in 2013 for the Miss Universe beauty pageant.

On Wednesday, Aras Agalarov claimed the story was invented. “I think this is some sort of fiction. I don’t know who is making it up,” he told Russia’s Business FM radio station, adding: “What has Hillary Clinton got to do with anything? I don’t know.”

Agalarov added that “I really don’t know Rob Goldstone well”. Goldstone, however, has travelled to Moscow and Baku – where Agalarov has a fan base – on numerous occasions and appears to be the singer’s concert promoter. Photos of the two of them appear on Goldstone’s Facebook page, including from a meeting in May 2015 with Trump at Trump Tower.